The present invention relates to a variable valve timing control apparatus of an internal combustion engine, which variably controls open and closing timing of an intake valve and/or an exhaust valve of the engine in accordance with an engine operating condition, and relates to a method for assembling the variable valve timing control apparatus.
A generally used vane type variable valve timing control apparatus is configured so that, in a state in which an application force by a hydraulic pressure does not act on the variable valve timing control apparatus upon stop of the engine, a vane rotor is relatively rotated to a retarded angle side with respect to a timing sprocket due to an alternating torque occurring at a camshaft.
However, in some variable valve timing control apparatuses, it is required that the valve timing upon stop of the engine, namely a position of the vane rotor upon stop of the engine, be an advanced angle position with respect to a most-retarded angle position. To meet this requirement, a related art has suggested that the vane rotor be forced in an advanced angle direction with respect to a housing by a spring force of a torsion spring.
For instance, in Japanese Patent Provisional Publication No. 2005-155346 (hereinafter is referred to as “JP2005-155346”), one end of the torsion spring is engaged with and fixed in a retaining groove that is formed on an end surface of the vane rotor, while the other end of the torsion spring is held by a retaining portion that is provided at the housing.
Further, at an outer circumferential side of the torsion spring, in order that the torsion spring does not easily come out when twisted in a diameter-reducing direction (in a direction that reduces a diameter of the torsion spring) after its installation, a cylindrical spring guide that extends from the vane rotor in an axial direction is provided.
Regarding assembly of a variable valve timing control apparatus in JP2005-155346, after each component or parts of the variable valve timing control apparatus is installed and assembled, the torsion spring is finally installed. Thus, the number of assembly process that takes place against an urging force (the spring force) of the torsion spring can be reduced to a minimum.